Transformer lead insulator and method of making same

ABSTRACT

High voltage lead insulator for shell-form transformers and method of constructing same. Hollow cylindrical members, being constructed of pressboard and having one of their ends flared, are coaxially positioned with respect to each other and are mounted over a circular opening in a U-shaped channel member. Adhesive is disposed between the flared surfaces to reinforce the structure.

United States Patent Lanoue et a1.

[451 July 11,1972

[54] TRANSFORMER LEAD INSULATOR AND METHOD OF MAKING SAME [72]Inventors: Thomas J. Lanoue, Muncie; John G. De

Neel, New Castle, both of Ind.

[73] Assignee: Westinghouse Electric Corporation, Pittsburgh, Pa.

[22] Filed: Aug. 2, 1971 [21] Appl. No.: 167,939

[52] U.S.Cl. ..174/138 R, 156/293, 174/167, 285/189, 285/D1G. 16 [51]Int. Cl ..H0lb 17/58, H0lf15/10, H01f27/32 [58] FieldofSearch ..174/l37R, 138 R, 138 E, 1526, 174/153 G, 167; 156/293; 285/189, 200, DIG. 16;336/192 [56] References Cited UNITED STATES PATENTS 2,425,443 8/1947Soreng ..336/ 192 FOREIGN PATENTS OR APPLICATIONS 611,557 3/1935 Germany..l74/l67 713,738 1l/l941 Germany ..336/l92 OTHER PUBLICATIONS Laib, PTs Are Getting Smaller, Allis-Chalmers Electrical Review, First Quarter1952, pages 20- 22.

Primary Examiner-Laramie E. Askin Attorney-A. T. Stratton et al.

57 ABSTRACT High voltage lead insulator for shell-form transformers andmethod of constructing same. Hollow cylindrical members, beingconstructed of pressboard and having one of their ends flared, arecoaxially positioned with respect to each other and are mounted over acircular opening in a U-shaped channel member. Adhesive is disposedbetween the flared surfaces to reinforce the structure.

6 Claims, 4 Drawing figures P'AfTENTEDJuL 11 m2, 3. 676-; 579

SHEET 2 OF 2 TRANSFORMER LEAD INSULATOR AND METHOD OF MAKING SAMEBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates, in general, to electrical inductive apparatus and, morespecifically, to lead insulating structures suitable for bringing out ahigh voltage lead from a shell-form power transformer winding.

2. Description of the Prior Art High power transformers, particularly ofthe shell-form type, require extensive insulation structure arrangementsto prevent corona discharges within the transformer. The insulationstructure which surrounds the high voltage lead of the transformerwinding is of particular importance. This structure must not onlyprovide sufficient dielectric strength in the region adjacent to thehigh voltage lead to prevent corona discharges, but it must also providesome structural support for the high voltage lead, which may berelatively large. In order to keep the lead from bending and comingclose to the other parts of the winding structure, an insulatedcylindrical tubular member is usually disposed over the high voltagelead and attached or secured to the insulation structure of the winding.Although this type of lead insulator performs satisfactorily, it is notreadily available in the United States. Lead insulators may be purchasedfrom foreign manufacturers, but because of complex construction detailsof the presently available lead insulators, the price for such isexcessive.

It therefore is desirable, and it is an object of this invention, toprovide a transformer lead insulator which may be easily constructedfrom inexpensive materials by semi-skilled personnel.

SUMMARY OF THE INVENTION The lead insulator disclosed herein isconstructed of pressboard members which are shaped to permit easyassembly and to provide an electrically and mechanically efficientstructure. A hollow cylindrical member, which has its lower end flared,is inserted through an opening in a U-shaped channel member. An adhesiveis disposed between the contacting surfaces. A second hollow cylindricalmember is telescoped over the first cylindrical member until the flaredportion of the second cylindrical member contacts the channel member. Asuitable adhesive is placed between the flared end and the channelmember, and between the two cylindrical members. Additional cylindricalmembers may be telescoped similarly if additional electrical and/ormechanical strength is desired.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages and uses of thisinvention will become more apparent when considered in view of thefollowing detailed description and drawings, in which:

FIG. 1 is a view of a shell-form transformer showing the placement ofthe lead insulator constructed according to the teachings of thisinvention;

FIG. 2 is a view of a lead insulator constructed according to theteachings of this invention;

FIG. 3 is an exploded view of a lead insulator constructed according tothe teachings of this invention illustrating the constructiontechniques; and

FIG. 4 is a partial cross-sectional view of the lead insulator shown inFIG. 2 and taken along the line IV-IV.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the followingdescription similar reference characters refer to similar members in allFigures of the drawmg.

Referring now to the drawings, and FIG. 1 in particular, there is showna laminated magnetic core of the shell-form type. The winding structure12, illustrated partially in phantom, includes a plurality of disk orpancake coils 14 which are 5 jects from the winding structure 12 and maybe connected to a high voltage bushing on the transformer casing. Thehigh voltage lead 18 extends through the lead insulator assembly 20which comprises the lead insulators 22 and 24. The lead insulator 22 isconstructed of a tubular member 26 and a channel member 28. The leadinsulator 24 is similarly constructed, except that the members whichform the lead insulator 24 have dimensions which permit its placementwithin the outer lead insulator 22. The channel member 28 includes sideportions which extend radially inward between the coils and/orinsulating spacers. Means, not shown, may be provided for securing thechannel member 28 to the winding structure 12.

The lead insulator assembly 20 provides structural support for the highvoltage lead as well as electrical insulation therefor. The number oflead insulators which are concentrically disposed depends largely on thesize, class, type and voltage rating of the transformer. Only one leadinsulator may be sufficient, or more than two lead insulators, asillustrated, may be necessary.

The lead insulator 22 is shown in FIG. 2 illustrating in greater detailthe shape of its members. The tubular member 26 is attached to thechannel member 28 by the joint 30. The channel member 28 includes thetop portion 32 and the side portions 34 and 36. The tubular member 26 ispositioned over a circular opening in the top portion 32 of the channelmember 28. The joint 30 is formed by the operations which are performedduring the construction of the lead insulator 22.

FIG. 3 is an exploded view of the lead insulator 22 shown in FIG. 2,illustrating the method of construction as taught by this invention. Thechannel member 28 is constructed of a suitable material, such aspressboard, and contains a circular opening 38, around which thepressboard has been cut and flared. The diameter of the opening 38,before flaring, is slightly less than the outside diameter of the hollowcylindrical member 40. The hollow cylindrical member 40 has its lowerend 42 flared as illustrated. The cylindrical member 40 is insertedthrough the opening 38 from the inside of the channel member 28 andpushed, upwardly as illustrated, until the flared end 42 contactsthe'inside of the flared opening flange 52. The cylindrical member 44also has a flared end 46. The inside diameter of the cylindrical member44 is slightly larger than the outside diameter of the cylindricalmember 40. This permits the cylindrical member 44 to be telescoped overthe cylindrical member 40, thus producing a structure laminated tubularmember. The cylindrical member 40 is pushed, downwardly as illustrated,until the flared end 46 contacts the flared opening flange 52. Ifadditional structural or dielectric strength is desired, anothercylindrical member, such as 48 with the flared end 50, may be telescopedover the cylindrical member 44. It is also within the contemplation ofthis invention that additional cylindrical members may be so telescoped.An adhesive material is applied between the flared portions of themembers, as well as between the surface walls of the cylindrical membersto bond the members together. Any suitable adhesive may be used, such aspressboard putty which comprises a mixture of polyvinyl chloride, waterand pressboard particles. A mixture of polyvinyl chloride, water andvirgin pulp particles may also be used.

Specific construction techniques are helpful in constructing leadinsulators according to this invention. For normally sized leadinsulators, the circular opening 38 in the channel member 28 may be cutwith a diameter which is three-eighths inch less than the outsidediameter of the cylindrical member 40. The pressboard adjacent to theopening 38 is moistened prior to being flared in order that thepressboard may be bent without cracking. The flared end portions of thecylindrical members are also moistened before being flared. The adhesivematerial is disposed on the outside of the flared end 42 and the insideof the flared opening flange 52. The cylindrical member 40 is insertedinto the opening until the flared end and the flange contact each otherand may be held firmly in this position until the adhesive has cured. Asuitable die or fixture may be inserted into the cylindrical member 40to help maintain its shape while drying.

The end 46 of the cylindrical member 44 is moistened and flared and thecylindrical member 44 is then telescoped over the cylindrical member 40,with an adhesive material disposed between the inside of the flared end46 and the outside of the flared opening flange 52. As the moistenedflanged end 46 dries, the pressboard shrinks, thereby compressing theadhesive material tightly into any irregularities which may exist aroundthe joint. A small amount of adhesive may be applied to the cylindricalmember 40 so that the two cylindrical members will be bonded together.

The end 50 of the cylindrical member 48 is moistened and flared. Thecylindrical member 48 is then telescoped over the cylindrical member,with an adhesive disposed between the contact areas of the flared ends46 and 50. An adhesive may also be applied to the outside of thecylindrical member 44 prior to the telescoping operation to bond the twocylinders together. A suitable adhesive may be packed around the outsideof the flared end 50 to reinforce the joint between the flared end 50and the channel member 28.

FIG. 4 is a partial cross-sectional view of the lead insulator shown inFIG. 2 and taken along the line IV-IV, illustrating, in detail, thevarious layers of pressboard and adhesive. The cylindrical members 40,44 and 48 are coaxially disposed, as shown, over the opening in the topportion 28 of the channel member. The flared end 42 is positioned underthe flared opening flange 52, with the adhesive 54 disposedtherebetween. The flared end 46 is positioned over the opening flange 52with the adhesive 56 disposed between their adjacent surfaces. Theadhesive 58 is similarly disposed between the adjacent surfaces of theflared ends 46 and 50, with the adhesive 60 disposed over the flared end50 to give the joint additional strength and smoothness.

Since numerous changes may be made in the abovedescribed apparatus anddifferent embodiments of the invention may be made without departingfrom the spirit thereof, it is intended that all of the matter containedin the foregoing description, or shown in the accompanying drawings,shall be interpreted as illustrative rather than limiting.

We claim as our invention:

1. A transformer lead insulator comprising a U-shaped channel memberhaving two sides and a top portion, a tubular member having first andsecond ends and a laminated wall, the first end of said tubular memberbeing attached by a suitable means to the top portion of said channelmember and positioned over a circular opening therein, said tubularmember comprising a plurality of hollow cylindrical members which arecoaxially positioned with respect to each other to form the laminatedtubular member wall.

2. The transformer lead insulator of claim 1, wherein the channel memberand the hollow cylindrical members are constructed of pressboard, with asuitable adhesive disposed between adjacent cylindrical members.

3. The transformer lead insulator of claim 1, wherein the means forattaching the tubular member comprises a joint which is formed by theends of the hollow cylindrical members and by the flared area of thechannel member which is adjacent to the opening therein, one end of afirst cylindrical member being flared and positioned adjacent to theinside of the flared channel member opening, one end of a secondcylindrical member being flared and positioned adjacent to the outsideof the flared channel member opening, with a suitable adhesive disposedbetween adjacent flare surfaces.

4. The transformer lead insulator of claim 3, wherein the adhesive whichis disposed between adjacent flare surfaces comprises a mixture ofpolyvinyl chloride, water and pressboard particles.

5. The transformer lead insulator of claim 3, wherein the adhesive whichis disposed between adjacent flare surfaces comprises a mixture ofpolyvinyl chloride, water and virgin pulp particles.

6. A method of constructing a transformer lead insulator comprising thesteps of:

providing two hollow cylindrical members, a first of said cylindricalmembers having an inside diameter which is slightly larger than theoutside diameter of the second cylindrical member, flaring one end ofsaid hollow cylindrical members, providing a U-shaped channel memberhaving a top portion,

cutting a circular opening in the top portion of said U- shaped channelmember, said opening having a diameter which is slightly less than theoutside diameter of the second cylindrical member, flaring the areaadjacent to the circular opening in the channel member, inserting thesecond cylindrical member into said opening from the inside of thechannel member, telescoping the first cylindrical member over the secondcylindrical member until the flare area of the first cylindrical memberis adjacent to the outside of the flare area around the opening in thechannel member, and applying an adhesive between the flared surfaces.

1. A transformer lead insulator comprising a U-shaped channel member having two sides and a top portion, a tubular member having first and second ends and a laminated wall, the first end of said tubular member being attached by a suitable means to the top portion of said channel member and positioned over a circular opening therein, said tubular member comprising a pluraLity of hollow cylindrical members which are coaxially positioned with respect to each other to form the laminated tubular member wall.
 2. The transformer lead insulator of claim 1, wherein the channel member and the hollow cylindrical members are constructed of pressboard, with a suitable adhesive disposed between adjacent cylindrical members.
 3. The transformer lead insulator of claim 1, wherein the means for attaching the tubular member comprises a joint which is formed by the ends of the hollow cylindrical members and by the flared area of the channel member which is adjacent to the opening therein, one end of a first cylindrical member being flared and positioned adjacent to the inside of the flared channel member opening, one end of a second cylindrical member being flared and positioned adjacent to the outside of the flared channel member opening, with a suitable adhesive disposed between adjacent flare surfaces.
 4. The transformer lead insulator of claim 3, wherein the adhesive which is disposed between adjacent flare surfaces comprises a mixture of polyvinyl chloride, water and pressboard particles.
 5. The transformer lead insulator of claim 3, wherein the adhesive which is disposed between adjacent flare surfaces comprises a mixture of polyvinyl chloride, water and virgin pulp particles.
 6. A method of constructing a transformer lead insulator comprising the steps of: providing two hollow cylindrical members, a first of said cylindrical members having an inside diameter which is slightly larger than the outside diameter of the second cylindrical member, flaring one end of said hollow cylindrical members, providing a U-shaped channel member having a top portion, cutting a circular opening in the top portion of said U-shaped channel member, said opening having a diameter which is slightly less than the outside diameter of the second cylindrical member, flaring the area adjacent to the circular opening in the channel member, inserting the second cylindrical member into said opening from the inside of the channel member, telescoping the first cylindrical member over the second cylindrical member until the flare area of the first cylindrical member is adjacent to the outside of the flare area around the opening in the channel member, and applying an adhesive between the flared surfaces. 